The present invention relates generally to an apparatus for treating a traveling textile material, particularly filament, yarn, or other strand-like material, in a pressurized fluid and, more particularly, to an apparatus for heating traveling textile strands to a heat-set temperature in a pressurized saturated steam atmosphere, such as preliminary to a texturizing operation.
In typical conventional apparatus for texturizing textile strands, a heating apparatus is provided through which the strand is directed to travel preliminarily to elevate the temperature of the strand to a predetermined heat-set temperature. One of the more common heating apparatus utilized for this purpose is a contact heater wherein the strand travels in a groove formed in a heating plate whose temperature is controlled to approximate the desired heat-set temperature. As is well-known, the temperature to which the strand is heated is a function not only of the temperature of the heating plate itself, but also the residence time spent by the traveling strand within the heater, which is determined by the traveling speed of the strand and the length of the groove formed in the heating plate. In recent years, the textile industry has increasingly demanded texturizing equipment capable of operating at ever higher strand traveling speeds, which objective has been addressed in basically two ways. First, texturizing equipment has been offered with heating apparatus of increasing lengths so as to achieve requisite strand residence times within the heaters and, in turn, sufficient heating to a desired heat-set temperature at increased strand traveling speeds. Second, more recently, texturizing equipment has become available utilizing heaters which generate a considerably higher strand-heating temperature than the desired heat-set temperature so as to accomplish sufficient strand heating within a shorter strand traveling distance while the strand travels at an elevated speed.
Disadvantages exist in both types of heating apparatus. More elongated heating apparatus of the first above-mentioned type may be as long as 2.5 meters and, accordingly, require considerably more space within the textile plant. Typically, to minimize the floor space occupied by such texturizing equipment, the heaters are oriented vertically, causing the apparatus to be of a considerable height. To attempt to reduce the height of texturizing equipment heaters, some equipment orient the heaters at an upward angle or, alternatively, configure the heaters to define an arcuate or circular strand traveling path. In either case, a greater floor space is occupied by the heating apparatus than with vertically-oriented heaters. Moreover, inclined or arcuate heaters additionally tend to cause a greater degree of frictional contact between the traveling strand and the groove within the heater plate which can produce damage to the traveling strand, cause excessive deposits of polymeric strand material and strand finishings to collect within the heater groove requiring periodic cleaning to maintain efficient heat transfer and minimize strand breakages, and otherwise deleteriously affect the texturizing process. It has also been found that more elongated heater sections in texturizing equipment can produce instabilities and surging within the strand heating zone, which does not typically occur in texturizing equipment whose heaters are shorter in length and operate at a lower strand traveling speed.
In texturizing equipment utilizing shorter length heaters operable at more elevated temperatures, often in the range of up to 600.degree. C., substantially greater energy must be generated to accomplish heating to such elevated temperatures, thereby correspondingly increasing the cost of operating the equipment. Furthermore, a greater risk exists in operating such equipment that the cross section of the strand can be rendered nonuniform by crystallizing the outermost portions of the strand to a greater degree than the strand core. The similar danger exists of severely damaging the strand by melting upon periodic stoppages of the equipment. Thus, it is critical in such equipment that the temperature of the heater and the traveling speed of the strand be closely monitored and carefully controlled to minimize these risks.
Similar disadvantages exist in conventional commercial equipment for heat-setting carpet yarns, wherein the objective is to stabilize the yarn bulk, to return the yarn to a fully relaxed state by relieving inner molecular tension within the strand structure, and to increase its crystallinity for better and more uniform dye pick-up. For this purpose, commercial carpet yarn heat-setting equipment typically accomplish heat-setting by directing the yarn to travel in a low tensioned state through a dry heat atmosphere or in a steam atmosphere at ambient pressure or a slightly elevated pressure. However, since the steam atmosphere generated in such equipment is typically at a temperature below a desired heat-setting temperature and since heat transfer from a dry heat atmosphere to a traveling strand is relatively inefficient, such conventional heat-setting equipment must be of a relatively significant length to achieve a sufficient dwell time of the traveling carpet yarn within the heater to obtain desired heat-setting results.